1. Field of the Invention
The invention lies in the field of electronic location determination. The invention relates to an optically based location system and a method for determining a location at a structure.
2. Description of the Related Art
In the recent past, the Federal Communications Commission (FCC) has promulgated standards related to the Emergency-911 (“E-911”) initiative. This initiative has set the initial standards for a communications system that, in the future, will precisely locate a particular person or object. Particularly, the initiative relates to precisely determining the location of a particular cellular telephone. As a result, location technologies have been developing rapidly. The rush to complete E-911, in particular, has compelled many cellular system designers to develop a scheme that will satisfy the location requirements set by the FCC.
Simultaneously, smaller-scale location opportunities, such as personal security and asset-management solutions, are being investigated. The smaller-scale location technologies present many more unsolved problems than the large-scale E-911 technology. One of the most challenging feats resides in the creation of technology that is able to locate a device within or around structures. As set forth herein, the terms “structure” or “structures” mean any enclosure, including, but not limited to, moveable enclosures, such as vehicles and robots. The terms do not necessarily include only man-made structures, such as buildings or cars, for example. An enclosure can have intermediate areas and walls. The term “areas” as used herein is defined as any subset of an enclosed space within or a defined space around a structure. An “area” can mean, for example, a small room with four walls and a door, or it can refer to a large room with many walls and doors and with intermediate cubicle-type half-walls. An “area” can also mean, for example, places adjacent a vehicle.
Equipment that uses radio frequency (“RF”) signals to capture Receive Signal Strength (“RSS”), Time Difference of Arrival (“TDoA”), or Angle of Arrival (“AoA”) clues have limited location accuracy and often require an expensive supporting infrastructure. RF location schemes such as RADAR, GPS, and LORAN have been used for years to locate people and/or objects outdoors. The realities of the indoor environment prevent RF schemes from being employed indoors. Specifically, when RF propagates in a building, the transmitted signal undergoes fading, dispersion, and interference with delayed versions of itself—otherwise known in the art as multipath interference. Such signal impediments make it extremely difficult to configure an indoor RF location system employing RSS, TDoA, or AoA for estimating a location of an object.
In most cases, existing optical in-building infrastructure includes already-installed lights, such as incandescent bulbs, fluorescent lamps, and halogen bulbs, or even LED's or laser diodes. These definitions for the term “light” or “lights” are not exclusive. A “light” can refer to any device used for visible light illumination or invisible light transmission, including, but not limited to, ultraviolet and infrared. Other existing devices include sensors, RF transceivers, and processors that can perform position estimates based on signal strength or some other ranging technology.
Various prior art devices and methods have used lighting for sending information in addition to providing illumination. The first four paragraphs of the background section of International PCT publication WO 99/53732 to Leeb et al. detail the progression of such devices and methods over the past few decades. These paragraphs are hereby incorporated herein by reference. None of the cited patents, however, provide the features of the invention.
For example, WO 99/53732 discloses an apparatus for modulating electromagnetic radiation to transmit information from a visible-light generating lamp such that human-perceptible flicker is eliminated regardless of the information content. WO 99/53732 does not address or disclose a system for locating an object in a building or using an optical detector in a system for locating an object in a building.
Additionally, International PCT publication WO 00/30415 to Lupton et al. discloses an electronic communications network that uses indoor fixtures, emitting modulated visible light, as transmitters that do not generate human-perceptible flicker. Using warning indicators, i.e., a speaker, the WO 00/30415 receiver indicates to a patient wearing the receiver whether or not that patient is within an authorized area. The WO 00/30415 photocell does not and cannot calculate its physical position with respect to a received light source based on the light it receives from that source. Thus, it cannot calculate a distance from a particular light source. The WO 00/30415 device also does not determine a relative or absolute position of a user from the light it receives. Further, WO 00/30415 only determines detectability within a given range from a light source.
Finally, International PCT publication WO 99/53633 to Hovorka et al. discloses a communications network similar to WO 00/30415 having an improved bandwidth using a particular coding scheme.